Frequency control in ultra high frequency circuit



April 2, 1946. c. N. SMYTH 2,397,701

FREQUENCY CONTROL IN ULTRA HIGH FREQUENCY CIRCUITS Filed Dec. 8, 1943- HT-l- Inventor Alto /la rney Patented Apr. 2, 1946 FREQUENCY CONTROL IN ULTRA HIGH FREQUENCY CIRCUIT Charles Norman Smyth, London, England, as-

signor, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware 7 Application December 8, 1943, Serial No. 513,355"

' In Great Britain February 20, 1940 7 Claims. (01. 250-36) This invention relates to thermionic ultra-highfrequency oscillation generators of the kind having a variable tuned regenerative feedback circuit between the anode and control grid and consisting of distributed impedances such as Lecher wires, co-axial lines and hollow resonators as opposed to tuned'circuits comprising lumped inductances and lumped capacity.

In such apparatus it is usually desirable to be able to adjust the frequency of the tuned circuit to adjust the oscillation frequency to precise predetermined values or to vary the frequency automatically or otherwise by very small amounts.

It is already known to vary an oscillation frequencyby altering the operating potentials of a thermionic valve coupled to the tuned circuit. It has also been proposed for frequency control or frequency adjustment to vary the dielectric constant in a capacityelement in a tuned circuit by varying the electronic space charge set up between two electrodes connected to the Lecher wires of a tuned circuit. It i now proposed for frequency control or frequency adjustment of an oscillation generator of the type specified to vary in the tuned circuit with distributed impedances the dielectric constant of said distributed impedances while maintaining the permeablity substantally constant. This may be done by varying the distribution and/or density of an electronic space charge set up between the conductors or conducting parts having the distributed impedances.

In one form of the invention the tuned circuit comprises a pair of Lecher wires varied in effective electrical length and characteristic impedance by means of the space charge in a vacuum tube. The vacuumtube has two parallel conductors sealed in its envelope and these conductors are arranged as parts of or extension to the Lecher wires. Between the conductors in the vacuum tube are disposed electrodes for setting up a variable space charge. These electrodes normally comprise a thermionic cathode and a grid system. Alteration of the potential upon.

the parts or extensions of the Lecher wires within the vacuum tube is varied. Although the capacity is varied due to the change in electron distribution, the inductance of the Lecher system remains substantially unaffected, since the permeability of the dielectric and the efiective diameter of the wires are substantially unchanged.

The invention will be made clearer in the following description of one practical embodiment of the invention illustrated diagrammatically 1n the accompanying drawing comprising a single Referring to the drawing, quency oscillation generator is indicated at OSC and comprises a thermionic valve V having a tuned circuit connected between the anode A and grid G. This tuned circuit comprises Lecher wires -via the H. T.+ terminal and the Lecher wire Li,

and grid bias is obtained for the control grid by means of resistance RI in the grid-cathode circuit. This oscillator'circuit is of known type and it is considered unnecessary to give any further description in detail herein.

In accordance with the invention the frequency of the generator CS0 is controlled by varying in effect theelectrical length of the Lecher wires by means of a space charge. For this purpose the vacuum tube T is provided. This tube consists of a cathode K, control grid. GI, screen grid. G2 and the Lecher wires L3, L4 already referred to. These parallel conductors L3, L4 are sealed in the envelope of the tube T, and between them in the vacuum tube are disposed the electrodes, K, GI and G2 for setting up a. variable space charge. The cathode K is shown as indirectly heated from an alternating source of current. The Lecher wires L3, L4 are biassed sufliciently negative through resistance R by a potential applied at B3 to prevent them from drawing current during any part of the high frequency cycle. The screen grid G2 is maintained at a positive potential by a potential applied at Bl, while the control grid GI is kept at a negative potential by a potential applied at B2. A space charge is developed between the screen grid and the Lecher wires and dependsupon the potentials on the grids or the potentials upon the conductors of the Lecher system; the efiective capacity between the Lecher wires is dependent upon this space charge and may thus be varied by varying the potentials on the screen grid or control grid or the Lecher wires or more than one of these members, thereby altering the tuning of the anode-grid circuit of the oscillation generator OSC and therefore the frequency generated.

The arrangement is particularly suitable for automatic frequency regulation since a voltage varying in accordance with fluctuations in frean ultra-high fretor may be employed to derive -aporrectingvoltage which in turn is applied in the manneride scribed to change the oscillator frequency to correct the intermediate frequency; i

In some cases the Lecher wires-n'lay;li'e vwholly outside the vacuum tube but losses then arise due to the presence. of the glass bulb in the dielectric space between the condllctors Similar efiects may also be obtained bybth provision of a thermionic cathode, with OLWith-zt out other electrodes, within a resonator of the hollow type; the; resonator; being evacuated or being enclosed in; a n-evacuatedbulh- Normally, such. cathode and l any 1 associated electrode are distinct and separate from, any thermionic system provided for the excitation of the resonator.

What is claimed is: .p r 1. A thermionic ultra-rhigh-frequency; oscillation generator; of the; kind, comprising-a tunedregenerative feedbackcircuit betweenthe anode and control grid consisting of, distributed ime pedances, including meansforysetting; up anelectronic space charge between at least-twoportions of said distributed impedances, saidi'means being separated from said impedances, andmeans for varying the distribution of i said electronic space charge, whereby the frequency-exhibited by said generator is-correspondinglyvaried;

2. Oscillation generator employing distributed impedance elements to determine-frequency, including means for setting up-an electronic space charge between-at least two portions of said distributed impeda'nces, saidmeans being separated from said impedances, andmeans for varying the density of said electronic'space charge, whereby the frequency exhibited by said generator is correspondinglyvaried, V l

3. Oscillation generator according to claim 1, in which said tuned circuit comprises a pair of Lecher wires and including a vacuum tube arranged so that said Lecher wires extend at least in part into operative juxtaposition therewith but spaced from the electrodes'thereo'f, said vacuum tube including means for varying the effective space charge between said Lecher wires.

4. Oscillation generator employing Lecher wires for frequency determination and including a vacuum tube arranged so that said Lecher wires extend at least in part into the interior of said tube butspaced from the electrodes thereof, said vacuum tube including means for varying the effective space charge between said Lecher wires.

5; Oscillation generator according to claim 4, andalsoincludinga co-axial group of electrodes for'producing; said space charge, located between the two conductors of said Lecher system, whereby the space charge is varied by varying the potential on at least one; of said electrodes;

6. Oscillation generator according to 1013111112; in which said distributed impedances comprise; Lecher wires and-also including a space chargevacuum tube, said Lecher wires extending at least partly outside said vacuum tube butclosely adjacent to the walls thereof wherebyalteration of the space charge withinsaid tube produces alteration of theefiective capacity between the portions of said Lecher wires adjacent to said vacuum tube.

7. Oscillation generator according to claim l, in which said distributed impedancescomprise Lecher wires and also includinga-space charge vacuumtube, said Lecher wires extending at least partly within said vacuum tube, said tube including within theenvelope-thereof a co-axial electrode structurecomprising an axial cathode and a, co-axial gridsystemandtwo rods sealed in the envelope toextend parallel to each other along opposite sides of the electrode structure, said electrode structure afiordingcontrol of said electronic space charge and said rodsacting as internal extensions of said Lecher wires,

CHARLES NORMAN SMYTH, 

